1. Field of the Invention
The invention in the field of immunology and immunotherapy is directed to peptides and their pharmaceutical compositions which are capable of preventing, suppressing or treating immune-related diseases. Specifically, the invention provides a therapy that results in clinical improvement of MS patients.
2. Description of the Background Art
Autoimmune diseases are characterized by an unwanted and unwarranted attack by the immune system on the tissues of the host. While the mechanism for progress of these diseases is not well understood, at least some of the details with respect to antigen presentation in this (and other) contexts are being elucidated. It is now thought that antigens, including autoantigens, are processed by antigen-presenting cells (APC), and the resulting fragments are then associated with one of the cell surface proteins encoded by the major histocompatibility complex (MHC). As a result, recognition of a peptide antigen is said to be MHC "restricted." When the MHC/antigen fragment complex binds to a complementary T cell receptor (TCR) on the surface of a T lymphocyte, it leads to activation and proliferation of the clone or subpopulation of T cells that bear that particular TCR. Once activated, T cells have the capacity to regulate other cells of the immune system which display the processed antigen and to destroy cells or tissues which carry epitopes of the recognized antigen.
A review of the role of TCRs in autoimmune diseases by Acha-Orbea et al. (Ann. Rev. Immunol. 7:371-405 (1989)) discussed the tremendous variation in TCRs available in the immune system of an individual and the generation of this diversity by germ line gene organization and rearrangement of the DNA encoding TCR .alpha. and .beta. chains. The .alpha. chains are encoded by various combinations of variable (V), junction (J) and constant (C) region gene segments. TCR .beta. chains are additionally encoded by a diversity (D) region gene segment, and, thus comprise a rearranged VDJC sequence. Due to allelic exclusion, a clone of T cells expresses only one type of TCR .alpha.-.beta. heterodimer.
A growing number of human diseases have been classified as autoimmune in nature (see, Theofilopoulos, A., In: D. P. Stites et al., eds., Basic and Clinical Immunology, Lange Medical Publications, Los Altos, Calif., 1988) of which several examples are rheumatoid arthritis (RA), myasthenia gravis (MG), multiple sclerosis (MS), systemic lupus erythematosus (SLE), autoimmune thyroiditis (Hashimoto's thyroiditis), Graves' disease, inflammatory bowel disease, autoimmune uveoretinitis, polymyositis and certain types of diabetes. Animal models have been developed for a number of these human autoimmune diseases. Among the best studied model is experimental allergic encephalomyelitis (EAE, also called experimental autoimmune encephalomyelitis), a model for MS.
Because it is now known that these and other autoimmune diseases involve the action of T helper cells stimulated by the binding of their TCR to an MHC/autoantigen (or non-autoantigen) complex, prevention and/or treatment strategies have been proposed which are based on the disruption of interactions between the MHC/antigen complex and the TCR. Wraith, D. C. et al., Cell 57:709-715 (1989)), proposed approaches based on this principle, including vaccination with whole T cells (as initially described by I. R. Cohen's laboratory, discussed below), passive blockade using antibodies which bind to the TCR, passive blockade using antibodies that bind to the MHC portion of the complex, administration of antibodies reactive with the T helper cell marker, CD4, and the use of peptides which mimic the antigen of interest and compete for binding to the MHC or the TCR molecule.
Myelin basic protein, MBP, is the major autoantigen involved in EAE and is the leading candidate as an encephalitogen involved in MS.
Heber-Katz's group (Heber-Katz, E. et al., Ann. N.Y. Acad. Sci. 540:576-577 (1988); Owhashi et al., J. Exp. Med. 168:2153-2164 (December 1988)) has analyzed the fine specificity of recognition of MBP epitopes by rat T cells. When T cells from rats immunized with MBP were hybridized to a mouse T lymphoma line and cloned, the pattern of fine specificity and Southern blot analysis of the TCR V.beta. gene rearrangement indicated a polyclonal response, even though 75% of the clones reacted to the 68-88 encephalitogenic determinant. A monoclonal antibody (mAb), designated 10.18, directed at one encephalitogenic T cell hybridoma proved to be an anti-idiotype or anti-clonotype which reacted only with T cell clones specific for the MBP 68-88 epitope. The mAb could block or reverse EAE when injected with, or 5 days after, the encephalitogenic MBP peptide. Soluble mAb 10.18 blocked the specific T cell clones, and immobilized mAb 10.18 stimulated their proliferation. Following induction of EAE with MBP, the proportion of mAb 10.18-binding cells increased from initially very low frequencies. The authors concluded that the 10.18.sup.+ T cells probably represent the dominant pathogenic T cell repertoire of EAE in Lewis rats. However, it was not known whether mAb 10.18 recognized a V region or an idiotypic determinant.
T cells expressing the TCR .alpha..beta. heterodimer can induce idiotypic and V gene family-specific antibodies that can regulate T cell function (Owhashi et al., supra; Gascoigne et al., Proc. Natl. Acad. Sci., USA 84:2936 (1987); Kappler et al., Nature 332:35 (1988); Kappler et al., Cell 49:263 (1987); MacDonald et al., Nature 332:40 (1988)). For example, antibodies that recognize the TCR V.beta.8 sequence have been effective in the prevention and treatment of autoimmunity in mice and rats (Owhashi et al., supra; Acha-Orbea et al., Cell 54:263-273 (1988); Urban et al., Cell 54:577-592 (1988)). Obtaining such antibodies selective for V region gene products has been dependent upon the availability of T cell clones that express TCR encoded by the relevant V gene family, and requires a laborious screening procedure using whole cells to establish specificity.
While antibody therapies in which antibodies are directed to MHC molecules and CD4 molecules have been generally successful in several animal models of autoimmunity, these approaches may be too nonspecific and potentially overly suppressive, since 70% of T cells bear the CD4 marker, and since all T cell-mediated responses and most antibody responses require MHC-associated antigen presentation.
Multiple sclerosis (MS) is an immune-mediated disease characterized by central nervous system mononuclear cell infiltration and demyelination. Although the pathogenesis of MS is unknown, both genetic and environmental factors have been implicated in the disease process. Major elements of the genetic predisposition include an association of disease with particular class II major histocompatibility complex (MHC) halotypes, in particular HLA-DR21 and -DQw1 (Terasaid et al., Science 1933:1245-1247 (976); Ho et al., Immunogenetics 15:509-517 (1982); Spielman et al., Epidemiol. Rev. 4:45-65 (1982); Francis et al., Lancet 1:211 (1986); Elian et al., Disease Markers 5:89-99 (1987)), as well as with certain polymorphisms within the T cell receptor (TCR) .alpha.-chain and .beta.-chain gene complexes (Beall et al., J. Cell. Biochem. 11D:223 (1987); Hauser et al., J. Neurol. 89:275-277 (1989); Seboun et al., Cell 57:1095-1100 (1989)). These studies suggest that the disease involves CD4.sup.+ T-cells bearing .alpha..beta. TCR. In support of this idea, CD4.sup.+ T cells represent a major component of mononuclear cells in the brains of active patients .alpha.-chain T cell receptors are present within central nervous system tissue of MS patients but not controls (Terasaid et al., Science 193:1245-1247 (976).
T lymphocytes that recognize myelin basic protein (BP) have been shown to have potent demyelinating and encephalitogenic activity in animals (Ben-Nun et al., Eur. J. Immunol. 11:195-199 (1981); McFarlin et al., New Eng. J. Med. 307:1183-1188 (1982); Mokhtarian et al., Nature 309:356-358 (1984); Vandenbark et al., J. Immunol. 135:223-228 (1985); Zamvil et al., Nature 317:355-358 (1985); Bourdette et al., Cell. Immunol. 112:351-363 (1988). Accumulating evidence also suggests that BP-specific T cells may contribute to the pathogenesis of MS. Thus, cells selected from MS patients on the basis of in vivo activation have specificity for BP. The frequencies of BP-reactive T cells are also increased in the blood and cerebrospinal fluid (CSF) of MS patients compared to normal individuals or patients with other neurological diseases. Furthermore, recent studies have demonstrated a marked selective enrichment of BP-reactive T cells in the CSF relative to the blood of individual MS patients. In animals, a limited set of TCR .alpha.-chain variable (V.alpha.) and .beta.-chain variable (V.beta.) genes are utilized by T cells specific for BP (Acha-Orbea et al., Cell 54:263-273 (1988); Urban et al., Cell 54:577-592 (1988); Burns et al., J. Exp. Med. 169:27-39 (1989); Heber-Katz et al., Immunol. Today 10:164-169 (1989)). Monoclonal antibodies directed to these regions or synthetic peptides with sequences common to these TCR variable regions can both protect and treat animals with clinical signs of experimental autoimmune encephalomyelitis (EAE) (Acha-Orbea et al., Cell 54:263-273 (1988); Urban et al., Cell 54:577-592 (1988); Vandenbark et al., Nature 341:541-544 (1989); Howell et al., Science 246:668-670 (1989)). In order for a similar approach to be applied to MS patients, it is critical to know if potentially pathogenic T cells also preferentially utilize a limited set of V region genes.
I. R. Cohen's laboratory has developed an approach to the immunospecific treatment of autoimmunity which utilizes whole live or attenuated T lymphocytes as vaccines to treat or prevent EAE, experimental autoimmune thyroiditis (EAT), and experimental arthritis. This approach is reviewed in Cohen, I. R., Immunol. Rev. 94:5-21 (1986), which discusses several animal models of autoimmune disease wherein vaccination with disease-specific T lymphocytes has been used to generate prophylactic or therapeutic effects. The fine specificity of vaccination was dictated by the fine specificity of the T cell recognition, possibly implicating the TCR. For example, two different anti-MBP T cell lines, each reactive to a different epitope of MBP, were found to vaccinate against EAE specifically induced by the particular epitope, indicating some form of anti-idiotypic immunity. However, when attempts were made to isolate clones of MBP-specific or thyroglobulin-specific T cells (in a thyroiditis model) from the non-clonal cell lines, only clones producing disease, but not resistance, were obtained. This led to the finding that appropriate aggregation or rigidification of cell membranes, by either hydrostatic pressure or chemical cross-linking, yielded cells which could induce protection more consistently. Similarly, low doses (sub-encephalitogenic) of MBP-specific cells could also induce resistance to lethal EAE. The protective state was termed "counter-autoimmunity." This state involves T cell clones which can specifically proliferate in response to the vaccinating T cells, can suppress effector clones in vitro (non-specifically, presumably through release of a suppressive lymphokine), and can adoptively transfer counter-autoimmunity in vivo. Such counter-autoimmunity is accompanied by suppressed delayed hypersensitivity (DH) responses to the specific epitope and prevention or remission of clinical disease.
A major difficulty with the foregoing approaches is that they require the use of complex biological preparations which do not comprise well-defined therapeutic agents. Such preparations suffer from complex production and maintenance requirements (e.g., the need for sterility and large quantities of medium for producing large number of "vaccine" T cells), and lack reproducibility from batch to batch. The T cell "vaccine" preparations, to be useful in humans, must be both autologous and individually specific, that is, uniquely tailored for each patient. Furthermore, the presence of additional antigens on the surface of such T cells may result in a broader, possibly detrimental, immune response not limited to the desired T cell clones (Offner et al., J. Neuroimmunol. 21:13-22 (1989).
There is a great need, therefore, for agents and pharmaceutical compositions which have the properties of specificity for the targeted autoimmune response, predictability in their selection, convenience and reproducibility of preparation, and sufficient definition to permit precise control of dosage.
Currently, no effective treatment for MS is known. (Harrison's Principles of Internal Medicine, 12th ed. Wilson et al., McGraw Hill, Inc. 1991). Therapeutic efforts are directed toward amelioration of the acute episode, prevention of relapses or progression of the disease, and relief of symptoms. The clinical manifestations of MS depend upon which nerve group or region of the brainstem, cerebellar or spinal cord is involved. Spinal cord involvement is the predominating feature in most advanced cases of MS.
In acute episodes of disease, glucocorticoid treatment has been suggested as having the potential to lessen the severity of symptoms and speed recovery, however, even its proponents point out that ultimate recovery is not improved by this drug nor is the extent of permanent disability altered. ACTH is the preferred glucocorticoid of clinicians since the only controlled trials which demonstrated any efficacy of glucocorticoid therapy in episodes of MS and optic neuritis were performed with this drug. However, use of long term steroids is not advised.
Immunosuppressive agents such as azathioprine and cyclophosphamide have been claimed to reduce the number of relapses in several series, but there is no consensus about the efficacy of these drugs either.
The current recommendations for the treatment of MS revolve around attempting to avoid exacerbation of the symptoms. Patients are advised to avoid excess fatigue and extremes of temperature and eat a balanced diet. (The above discussion is primarily from Chapter 356 of Harrison's Principles of Internal Medicine, 12th ed 1991.)